Light olefins serve as feed materials for the production of numerous chemicals. Light olefins have traditionally been produced through the processes of steam or catalytic cracking of hydrocarbons derived from petroleum sources. Fluidized catalytic cracking (FCC) of heavy hydrocarbon streams is commonly carried out by contacting relatively high boiling hydrocarbons with a catalyst composed of finely divided or particulate solid material. The catalyst is transported in a fluid-like manner by transmitting a gas or vapor through the catalyst at sufficient velocity to produce a desired regime of fluid transport. Contact of the oil with the fluidized catalyst results in the cracking reaction.
FCC processing is more fully described in U.S. Pat. Nos. 5,360,533, 5,584,985, 5,858,206 and 6,843,906. Specific details of the various contact zones, regeneration zones, and stripping zones along with arrangements for conveying the catalyst between the various zones are well known to those skilled in the art.
The FCC reactor serves to crack gas oil or heavier feeds into a broad range of products. Cracked vapors from an FCC unit enter a separation zone, typically in the form of a main column, that provides a gas stream, a gasoline cut, light cycle oil (LCO) and clarified oil (CO) which includes heavy cycle oil (HCO) components. The gas stream may include hydrogen and C1 and C2 hydrocarbons, and liquefied petroleum gas (“LPG”), i.e., C3 and C4 hydrocarbons.
There is an increasing need for light olefins such as ethylene for the production of polyethylene, ethyl benzene and the like as opposed to heavier olefins. Research efforts have led to the development of an FCC process that produces or results in greater relative yields of light olefins, e.g., ethylene. Such processing is more fully described in U.S. Pat. No. 6,538,169.
Ethyl benzene is an important intermediate compound for the production of styrene. Although often present in small amounts in crude oil, ethyl benzene is produced in bulk quantities by combining the petrochemicals benzene and ethylene in an acid or zeolite catalyzed chemical reaction. Catalytic dehydrogenation of the ethyl benzene then gives hydrogen gas and styrene.
A conventional FCC process produces a combined ethylene/ethane stream. The ethylene/ethane stream is typically run through a splitter or distillation column to separate the ethylene from the ethane. The operation of such a splitter is energy intensive in addition to construction and maintenance costs.
In view of the increasing need and demand for light olefins such as ethylene and the use thereof in producing ethyl benzene, there is a need and a demand for improved processing and arrangements for the separation and recovery of light olefins, such as ethylene, from such FCC process effluent and the efficient conversion of those olefins into useful aromatic intermediates, such as ethyl benzene.